Titanium dioxide(TiO2) has been used widely in the electronics, ceramics, catalysis, and pigment industries. Recently, the research is focusing on the nano-sized TiO2 to improve its photo-catalytic activity for removal of environmental pollutants. N doped TiO2 powers were studied extensively with purpose of extending the absorption spectrum to visible light. In this study, we prepared high quality nano-sized N doped TiO2 powders using DC plasma jet in order to improve the photocatalytic activity. Nitrogen gas, reacting gas oxygen and titanium tetrachloride(TiCl4) were infected into the plasma reactor. The absorption spectra of synthesized TiO2 powedrs shifted from UV region to visible region according to thd introduction of nitrogen. The experimental results of acetaldehyde deconposition shown that photocatalytic activity of N-doped TiO2 is higher than that of pure TiO2.